COMMUNICATIONS DEVICE AND METHOD
TECHNICAL FIELD OF THE DISCLOSURE
The present disclosure relates to mobile communications systems, network elements such as
such base stations for use in mobile communications systems, methods of communicating using
mobile communications systems and communications devices.
BACKGROUND OF THE DISCLOSURE
Third and fourth generation mobile telecommunication systems, such as those based on the
3GPP defined UMTS and Long Term Evolution (LTE) architecture are able to support more
sophisticated services than simple voice and messaging services offered by previous generations of
mobile telecommunication systems.
For example, with the improved radio interface and enhanced data rates provided by LTE
systems, a user is able to enjoy high data rate applications such as mobile video streaming and mobile
video conferencing that would previously only have been available via a fixed line data connection.
The demand to deploy third and fourth generation networks is therefore strong and the coverage area
of these networks, i.e. geographic locations where access to the networks is possible, is expected to
increase rapidly.
The anticipated widespread deployment of third and fourth generation networks has led to the
parallel development of a class of devices and applications which, rather than taking advantage of the
high data rates available, instead take advantage of the robust radio interface and increasing ubiquity
of the coverage area. Examples include so-called machine type communication (MTC) applications,
which are typified by semi-autonomous or autonomous wireless communication devices (i.e. MTC
devices) communicating small amounts of data on a relatively infrequent basis. Examples include socalled
smart meters which, for example, are located in a customer's house and periodically transmit
information back to a central MTC server data relating to the customers consumption of a utility such
as gas, water, electricity and so on.
Whilst it can be convenient for a device such as an MTC type device to take advantage of the
wide coverage area provided by a third or fourth generation mobile telecommunication network there
are at present disadvantages. Unlike a conventional third or fourth generation mobile device such as a
smartphone, an MTC-type device is preferably relatively simple and inexpensive. The type of
functions performed by the MTC-type device (e.g. collecting and reporting back data) do not require
particularly complex processing to perform. However, third and fourth generation mobile
telecommunication networks typically employ advanced data modulation techniques on the radio
interface which can require more complex and expensive radio transceivers to implement. It is usually
justified to include such complex transceivers in a smartphone as a smartphone will typically require a
powerful processor to perform typical smartphone type functions. However, as indicated above, there
is now a desire to use relatively inexpensive and less complex devices to communicate using LTE type
networks.
SUMMARY OF THE DISCLOSURE
According to a first aspect of the present disclosure there is provided a mobile
communications system for communicating data to and/or from mobile communications devices. The
mobile communications system comprises one or more base stations, each of which includes a
transmitter and a receiver configured to provide a wireless access interface for communicating data to
and/or from the mobile communications devices, the wireless access interface providing on a
downlink a first carrier, the first carrier providing a plurality of communications resource elements
across a first frequency range for communicating data and providing a plurality of communications
resource elements within a second frequency range which is within and smaller than the first
frequency range forming a second carrier. First mobile communications devices being full capability
devices are configured to receive signals transmitted via the first carrier within the first frequency
range, and second mobile communications devices being reduced capability devices are configured to
receive signals transmitted via the second carrier within the second frequency range. The wireless
access interface provided by the base stations includes a plurality of time divided sub-frames, each
sub-frame including the plurality of communications resource elements of t e first frequency range
and the plurality of the communications resource elements of the second frequency range, and each
sub-frame includes a first wideband control channel in a part of each sub-frame having a bandwidth
corresponding substantially to the first frequency range, and a second narrow band control channel in a
second part of each sub-frame and having a bandwidth which is less than the first wideband control
channel and a duration of the second narrow band control channel within the sub-frame is greater than
a duration of the first wideband control channel within the sub-frame. The second narrow band
control channel is configured for communicating control information to both the first mobile
communications devices and the second mobile communications devices and forms part of the
plurality of the communications resource elements of the second frequency range of the virtual carrier.
By arranging for t e narrow band control channel to be within the virtual carrier and to
communicate control information to both the first and the second mobile communications devices, the
second reduced capability devices can access the narrow band control channel which is shared with the
first full-capability mobile devices. This arrangement makes more efficient use of the
communications resources available to the communications system.
In conventional mobile telecommunication networks, data is typically transmitted from the
network to the mobile devices in a frequency carrier (first frequency range) where at least part of the
data spans substantially the whole of the bandwidth of the frequency carrier. Normally a mobile device
cannot operate within the network unless it can receive and decode data spanning the entire frequency
carrier, i.e. a maximum system bandwidth defined by a given telecommunication standard, and
therefore the use of mobile devices with reduced bandwidth capability transceiver units is precluded.
However, as disclosed in co-pending International patent applications numbered
PCT/GB20 12/0502 13, PCT/GB20 12/0502 14, PCT/GB20 12/050223 and PCT/GB20 12/05 1326 , the
contents of which are herein incorporated by reference, a subset of the communications resource
elements comprising a conventional carrier (a "host carrier") are defined as a "virtual carrier", where
the host carrier has a certain bandwidth (first frequency range) and where the virtual carrier has a
reduced bandwidth (second frequency range) compared to the host carrier's bandwidth. Data for
reduced capability devices is separately transmitted on the virtual carrier set of communications
resource elements. Accordingly, data transmitted on the virtual carrier can be received and decoded
using a reduced complexity or capability transceiver unit.
Devices provided with reduced complexity or capability transceiver units (onwards referred to
as "reduced capability devices") could operate by using a part of its full capability (i.e. reduced
capability set of its full capability) or they could be constructed to be less complex and less expensive
than conventional LTE type devices (onwards referred to generally as LTE devices). Accordingly, the
deployment of such devices for MTC type applications within an LTE type network can become more
attractive because the provision of the virtual carrier allows mobile devices with less expensive and
less complex transceiver units to be used.
It is currently being proposed to provide mobile communications systems, such as LTE for
example, in which a plurality of sub-carrier are divided in time to provide sub-frames. Each sub-frame
may include a wide band control channel region for transmitting a control channel for granting access
to shared communications resources and may also include at least one narrow band control channel
region which has a narrower bandwidth than the wide band control channel region but has a longer
time duration and can be used to transmit a further control channel to communicate the same
information or different information for the same purpose as the control channel information
communicated on the wide band control channel. In one embodiment the narrow band control channel
region has a duration which extends over substantially all of the remainder of a sub-frame after the
wide band control channel region. The arrangement of a narrow band control channel region within a
sub-frame together with a wide band control channel region has been proposed because the wide band
control channel region could exist in the same part of t e sub-frame of a wireless access interface and
across all sub-carriers in the frequency band of the host carrier. Accordingly, it is possible that two
base stations of neighbouring cells are transmitting different control channel information in the wide
band control channel region contemporaneously which could, therefore interfere with each other.
Accordingly, by providing a narrow band control channel region within each sub-frame which can be
in a different location in frequency in the neighbouring cells, covering a different set of sub-carriers,
for example, then control information can be communicated to mobile devices within different cells
with a reduced potential for causing co-channel interference. Such an arrangement for example for
LTE is being proposed in 3GPP. Within LTE therefore the wide band control channel is referred to as
the Physical Downlink Control Channel (PDCCH) whereas the narrow band control channel is
referred to as the Enhanced Physical Downlink Control Channel (EPDCCH), which is studied under
the 3GPP work item "Enhanced downlink control channel(s) for LTE".
Embodiments of the present disclosure can provide an arrangement in which reduced
capability mobile devices of a second type exist within a cell served by a base station with full
capability devices of a first type and in which both a wide band control channel region and a narrow
band control channel region is provided by a wireless access interface to the first and second types of
mobile devices. The base station arranges for the wireless access interface to locate the narrow band
control region within a second frequency range providing a virtual carrier which exists within a host
carrier covering a first frequency range, the first frequency range including the second frequency
range. Thus, a scheduler for example of the base station is adapted to locate the narrow band control
channel (EPDCCH) as part of a virtual carrier within the second frequency range so that devices of the
second type are able to receive control information granting access to communications resources from
the narrow band control channel as well as devices of the first type also being granted access to
communications resources from the narrow band control channel. However, as a result of the reduced
capability of the mobile devices of the second type, the narrow band control channel grants access to
communications resources only within the second frequency range whereas full capability devices of
the first type may be granted access to shared resources within the first frequency range of the host
carrier. Accordingly, the co-existence of full capability mobile devices of the first type with reduced
capability mobile devices of the second type which receive control information granting access to
communications resources from the same narrow band control channel provides an arrangement which
efficiently uses communications resources available to the communications systems.
As will be appreciated because the reduced capability mobile devices of the second type only
receive signals communicated within the second frequency range which is less than the first frequency
range, so that the mobile devices of the second type cannot receive control information communicated
on the wide band control channel. In one example the wide band control channel may communicate
control information to mobile devices within a cell served by the base station which is required by the
mobile devices to both transmit and receive information in the communications resources provided by
the base station. According to one embodiment the control information is repeated and also
transmitted in a separate control channel within the second frequency range of the virtual carrier. In
one example the control information is what is known as Common Search Space (CSS) information
which would be required by mobile devices to access the communications resources provided by the
base station.
Various further aspects and embodiments of the disclosure are provided in the appended
claims, including but not limited to, a mobile communications system network element for
communicating data to and/or from mobile communications devices, used in a mobile communications
network and a method of communicating data to and/or from mobile communications devices in a
mobile communications system.
BRIEF DESCRIPTION OF DRAWINGS
Embodiments of the present disclosure will now be described by way of example only with
reference to the accompanying drawings in which like parts are provided with corresponding reference
numerals and in which:
Figure 1 provides a schematic diagram illustrating an example of a conventional mobile
communications system;
Figure 2 provides a schematic diagram illustrating a conventional LTE downlink radio frame;
Figure 3 provides a schematic diagram illustrating a conventional LTE downlink radio subframe;
Figure 4 provides a schematic diagram illustrating an LTE downlink radio sub-frame in which
a virtual carrier has been inserted;
Figure 5 provides a schematic diagram illustrating an example of an LTE downlink radio subframe
which includes a narrow band control channel for a localised application;
Figure 6 provides a schematic diagram illustrating an example of an LTE downlink radio subframe
which includes a narrow band control channel for a distributed application;
Figure 7 provides a schematic diagram illustrating an example of an LTE downlink radio subframe
in which a virtual carrier is provided and includes a narrow band control channel in accordance
with an example embodiment;
Figure 8 provides a schematic diagram illustrating an example of an LTE downlink radio subframe
in which a virtual carrier is provided and includes a narrow band control channel in accordance
with an example embodiment;
Figure 9 provides a schematic diagram illustrating an example of an LTE downlink radio subframe
in which a virtual carrier is provided and includes a distributed narrow band control channel in
accordance with an example embodiment;
Figure 10 provides a schematic diagram illustrating an example of an LTE downlink radio
sub-frame in which a virtual carrier is provided and includes a distributed narrow band control channel
in accordance with an example embodiment;
Figure 1 1 provides a schematic diagram illustrating an example of an LTE downlink radio
sub-frame in which two virtual carriers are provided and includes a distributed narrow band control
channel in accordance with an example embodiment;
Figure 12 provides a schematic diagram illustrating an example of an LTE downlink radio
sub-frame which includes narrow band control channels for both localised and distributed applications
in accordance with an example embodiment;
Figure 13 provides a schematic diagram illustrating an example of an LTE downlink radio
sub-frame in which a virtual carrier is provided and includes a narrow band control channel as well as
a control channel for providing Common Search Space information in accordance with an example
embodiment;
Figure 14 provides a schematic diagram illustrating an example of an LTE downlink radio
sub-frame in which a virtual carrier is provided and includes a narrow band control channel as well as
a control channel for providing Common Search Space information in accordance with an example
embodiment;
Figure 15 provides a schematic diagram illustrating an example of an LTE downlink radio
sub-frame in which a virtual carrier is provided and includes a narrow band control channel as well as
a control channel for providing Common Search Space information in accordance with an example
embodiment; and
Figure 16 provides a schematic diagram showing part of an adapted LTE mobile
telecommunication network arranged in accordance with an example of the present disclosure.
DESCRIPTION OF EXAMPLE EMBODIMENTS
Conventional Network
Figure 1 provides a schematic diagram illustrating the basic functionality of a conventional
mobile communications system.
The network includes a plurality of base stations 101 connected to a core network 102. Each
base station provides a coverage area 103 (i.e. a cell) within which data can be communicated to and
from mobile devices 104. Data is transmitted from a base station 101 to a mobile device 104 within a
coverage area 103 via a radio downlink. Data is transmitted from a mobile device 104 to a base station
101 via a radio uplink. The core network 102 routes data to and from the base stations 104 and
provides functions such as authentication, mobility management, charging and so on.
The term mobile devices will be used to refer to a communications terminal or apparatus
which can transmit or receive data via the mobile communications system. Other terms may also be
used for mobile devices such as communications terminal, remote terminal, transceiver device or user
equipment which may or may not be mobile.
Mobile telecommunications systems such as those arranged in accordance with the 3GPP
defined Long Term Evolution (LTE) architecture use an orthogonal frequency division multiplex
(OFDM) based radio access interface for the radio downlink (so-called OFDMA) and the radio uplink
(so-called SC-FDMA). Data is transmitted on the uplink and on the downlink on a plurality of
orthogonal sub-carriers. Figure 2 shows a schematic diagram illustrating an OFDM based LTE
downlink radio frame 201. The LTE downlink radio frame is transmitted from an LTE base station
(known as an enhanced Node B) and lasts 10 ms. The downlink radio frame comprises ten sub-frames,
each sub-frame lasting 1 ms. A primary synchronisation signal (PSS) and a secondary synchronisation
signal (SSS) are transmitted in the first and sixth sub-frames of the LTE frame, in the case of
frequency division duplex (FDD) system. A primary broadcast channel (PBCH) is transmitted in the
first sub-frame of the LTE frame. The PSS, SSS and PBCH are discussed in more detail below.
Figure 3 provides a schematic diagram providing a grid which illustrates the structure of an
example of a conventional downlink LTE sub-frame. The sub-frame comprises a predetermined
number of symbols which are transmitted over a 1ms period. Each symbol comprises a predetermined
number of orthogonal sub-carriers distributed across the bandwidth of the downlink radio carrier.
The example sub-frame shown in Figure 3 comprises 14 symbols and 1200 sub-carriers
spaced across a 20MHz bandwidth. The smallest unit on which data can be transmitted in LTE is
twelve sub-carriers transmitted over one sub-frame. For clarity, in Figure 3, each individual resource
element is not shown, instead each individual box in the sub-frame grid corresponds to twelve subcarriers
transmitted on one symbol.
Figure 3 shows resource allocations for four LTE devices 340, 341, 342, 343. For example,
the resource allocation 342 for a first LTE device (UE 1) extends over five blocks of twelve subcarriers,
the resource allocation 343 for a second LTE device (UE2) extends over six blocks of twelve
sub-carriers and so on.
Control channel data is transmitted in a control region 300 of the sub-frame comprising the
first n symbols of the sub-frame where n can vary between one and three symbols for channel
bandwidths of 3MHz or greater and where n can vary between two and four symbols for channel
bandwidths of 1.4MHz. For clarity, the following description relates to host carriers with channel
bandwidth of 3MHz or greater where the maximum value of n will be 3 . The data transmitted in the
control region 300 includes data transmitted on the physical downlink control channel (PDCCH), the
physical control format indicator channel (PCFICH) and the physical HARQ indicator channel
(PHICH).
The PDCCH contains control data indicating which sub-carriers on which symbols of the subframe
have been allocated to specific LTE devices. Thus, the PDCCH data transmitted in the control
region 300 of the sub-frame shown in Figure 3 would indicate that UE1 has been allocated the first
block of resources 342, that UE2 has been allocated the second block of resources 343, and so on. In
subframes where it is transmitted, the PCFICH contains control data indicating the duration of the
control region in that subframe (i.e. between one and four symbols) and the PHICH contains HARQ
(Hybrid Automatic Request) data indicating whether or not previously transmitted uplink data has
been successfully received by the network.
In certain sub-frames, symbols in a central band 310 of the sub-frame are used for the
transmission of information including the primary synchronisation signal (PSS), the secondary
synchronisation signal (SSS) and the physical broadcast channel (PBCH). This central band 310 is
typically 72 sub-carriers wide (corresponding to a transmission bandwidth of 1.08 MHz). The PSS
and SSS are synchronisation signals that once detected allow the LTE device 104 to achieve frame
synchronisation and determine the cell identity of the enhanced Node B transmitting the downlink
signal. The PBCH carries information about the cell, comprising a master information block (MIB)
that includes parameters that the LTE devices require to access the cell. Data transmitted to individual
LTE devices on the physical downlink shared channel (PDSCH) can be transmitted in the remaining
blocks of communications resource elements of the sub-frame.
Figure 3 also shows a region of PDSCH containing system information and extending over a
bandwidth of R344 .
The number of sub-carriers in an LTE channel can vary depending on the configuration of the
transmission network. Typically this variation is from 72 sub carriers contained within a 1.4MHz
channel bandwidth to 1200 sub-carriers contained within a 20MHz channel bandwidth as shown in
Figure 3. As is known in the art, data transmitted on the PDCCH, PCFICH and PHICH is typically
distributed on the sub-carriers across the entire bandwidth of the sub-frame. Therefore a conventional
LTE device must be able to receive the entire bandwidth of the sub-frame in order to receive and
decode the control region.
Virtual Carrier
Certain classes of devices, such as MTC devices (e.g. semi-autonomous or autonomous
wireless communication devices such as smart meters as discussed above), support communication
applications that are characterised by the transmission of small amounts of data at relatively infrequent
intervals and can thus be considerably less complex than conventional LTE devices. In many
scenarios, providing reduced capability devices such as those with a conventional high-performance
LTE receiver unit capable of receiving and processing data from an LTE downlink frame across the
full carrier bandwidth can be overly complex for a device which only needs to communicate small
amounts of data. This may therefore limit the practicality of a widespread deployment of reduced
capability MTC type devices in an LTE network. It is preferable instead to provide reduced capability
devices such as MTC devices with a simpler receiver unit which is more proportionate with the
amount of data likely to be transmitted to the device. As set out below, in accordance with examples of
the present disclosure a "virtual carrier" is inserted in a conventional OFDM type downlink carrier (i.e.
a "host carrier") as a carrier with a limited frequency bandwidth narrower than that of the host carrier.
Unlike data transmitted on a conventional OFDM type downlink carrier, data transmitted on the virtual
carrier can be received and decoded without needing to process the full bandwidth of the downlink
host OFDM carrier. Accordingly, data transmitted on the virtual carrier can be received and decoded
using a reduced complexity receiver unit.
Figure 4 provides a schematic diagram illustrating an LTE downlink sub-frame which
includes a virtual carrier inserted in a host carrier in accordance with an example of the present
disclosure.
In keeping with a conventional LTE downlink sub-frame, the first n symbols (n is three in
Figure 4) form the control region 300 which is reserved for the transmission of downlink control data
such as data transmitted on the PDCCH. However, as can be seen from Figure 4, outside of the control
region 300 the LTE downlink sub-frame includes a group of communications resource elements below
the central band 310 which form a virtual carrier 501. As will become clear, the virtual carrier 501 is
adapted so that data transmitted on the virtual carrier 501 can be treated as logically distinct from the
data transmitted in the remaining parts of the host carrier and can be decoded without first decoding all
the control data from the control region 300. Although Figure 4 shows the virtual carrier occupying
frequency resources below the centre band, in general the virtual carrier can alternatively either
occupy frequency resources above the centre band or frequency resources including the centre band. If
the virtual carrier is configured to overlap any resources used by the PSS, SSS or PBCH of the host
carrier, or any other signal transmitted by the host carrier that a mobile device operating on the host
carrier would require for correct operation and expect to find in a known pre-determined location, the
signals on the virtual carrier can be arranged such that these aspects of the host carrier signal are
maintained.
As can be seen from Figure 4, data transmitted on the virtual carrier 501 is transmitted across
a limited bandwidth. This could be any suitable bandwidth providing it is smaller than that of the host
carrier. In the example shown in Figure 4 the virtual carrier is transmitted across a bandwidth
comprising 12 blocks of 12 sub-carriers (i.e. 144 sub-carriers) which is equivalent to a 2.16MHz
transmission bandwidth. Accordingly, a device receiving data transmitted on the virtual carrier need
only be equipped with a receiver capable of receiving and processing data transmitted over a
bandwidth of 2.16MHz. This enables reduced capability devices (for example MTC type devices) to
be provided with simplified receiver units yet still be able to operate within an OFDM type
communication network which, as explained above, conventionally requires devices to be equipped
with receivers capable of receiving and processing an OFDM signal across the entire bandwidth of the
signal.
As explained above, in OFDM based mobile communication systems such as LTE, downlink
data is dynamically assigned to be transmitted on different sub-carriers on a sub-frame by sub-frame
basis. Accordingly, in every sub-frame the network must signal which sub-carriers on which symbols
contain data relevant to which devices (i.e. downlink allocation signalling).
As can be seen from Figure 3, in a conventional downlink LTE sub-frame this information is
transmitted on the PDCCH during the first symbol or symbols of the sub-frame. However, as
previously explained, the information transmitted in the PDCCH is spread across the entire bandwidth
of the sub-frame and therefore cannot be received by a mobile communication device with a simplified
receiver unit capable only of receiving the reduced bandwidth virtual carrier.
Accordingly, as can be seen in Figure 4, the final symbols of the virtual carrier can be reserved
as a virtual carrier control region 502 which is allocated for the transmission of control data indicating
which communications resource elements of the virtual carrier 501 have been allocated. In some
examples the number of symbols comprising the virtual carrier control region 502 can be fixed for
example symbols..
The virtual carrier control region can be located at any suitable position within the virtual
carrier for example in the first few symbols of the virtual carrier. In t e example of Figure 4 this could
mean positioning the virtual carrier control region on the fourth, fifth and sixth symbols. However,
fixing the position of the virtual carrier control region in the final symbols of the sub-frame can
provide an advantage because the position of the virtual carrier control region need not vary even if the
number of symbols of the host carrier control region varies. This simplifies the processing undertaken
by mobile communication devices receiving data on the virtual carrier because there is no need for
them to determine the position of the virtual carrier control region every sub-frame as it is known that
it will always be positioned in the final symbols of the sub-frame.
In a further example, the virtual carrier control symbols may reference virtual carrier PDSCH
transmissions in a separate sub-frame.
In some examples the virtual carrier may be located within the centre band 310 of the
downlink sub-frame. This would minimise the reduction in host carrier PDSCH resources caused by
the insertion of a virtual carrier since the resources occupied by the PSS/SSS and PBCH would be
contained within the virtual carrier region and not the host carrier PDSCGH region. Therefore,
depending on for example the expected virtual carrier throughput, the location of a virtual carrier can
be appropriately chosen to either exist inside or outside the centre band according to whether the host
or virtual carrier is chosen to bear the overhead of the PSS, SSS and PBCH.
Narrow Band Control Channel
Embodiments of the present disclosure provide an arrangement in which a narrow band
control channel which is common to both the full capability (LTE) mobile devices of a first type and
reduced capability devices of a second type. The information transmitted on the control channel in the
narrow band control region is the same as or similar to the information transmitted on the wide band
control channel in the wide band control region which co-exists within a sub-frame of the wireless
access interface. Such an arrangement which is currently being proposed in 3GPP is known as the
EPDCCH which exists together with the PDCCH, which is a wide band control channel. An example
arrangement is illustrated in Figure 5.
In Figure 5 a simplified version of a downlink sub-frame for an LTE system with respect to
the example of Figure 4 is presented. In Figure 5 the control region 300 is shown in a corresponding
position in which it appears in Figure 4 and contains the PDCCH which communicates messages to
mobile devices allocating communications resources which are shared by all full capability mobile
devices. As shown in Figure 5 a narrow band control channel region 600 is provided, which for LTE
contains the EPDCCH. The narrow band control channel 600 communicates resource allocation
messages to mobile devices. However, the narrow band control channel region is narrower in
frequency than the wide band control channel region 300 and extends for substantially the entire subframe
after the transmission of the wide band control channel 300. Hereinafter the narrow band
control channel will be referred to as the EPDCCH and the wide band control channel is referred to as
the PDCCH although the skilled person will appreciate that these are just examples of respective wide
band and narrow band control channels, which are applicable for the LTE example.
As explained above the purpose of providing the EPDCCH 600 is to achieve communicating
resource allocation messages to mobile devices in a way which reduces a likelihood of causing intercell
interference for the transmission of control channels. As will be seen in Figure 5 the PDCCH 300
occurs at the same part in the sub-frame for the entire band width of the sub-frame, for each subframe.
Therefore, if two or more base stations of neighbouring cells are transmitting respective
PDCCHs, these could potentially interfere because the PDCCH occurs at the same point in the subframe
and across the entire band width of the system. Accordingly, it has been proposed to provide
t e EPDCCH 600 which extends across the entire sub-frame, and, as a narrow band control channel,
can be located in different sub-carriers for neighbouring base stations. Accordingly, a probability of
inter-cell interference is therefore reduced.
The arrangement shown in Figure 5 is referred to as a localised EPDCCH 600 because the
EPDCCH is transmitting control information to the mobile devices 104 within a cell 103. The
arrangement shown in Figure 6 is an alternative architecture for an EPDCCH having first and second
parts at different frequencies 602, 604. The arrangement of the EPDCCH 602, 604 shown in Figure 6
provides some frequency diversity for the transmission of control information via the EPDCCH.
Thus, the same information can be transmitted on the EPDCCH 602, 604 of Figure 6 as that
transmitted by the EPDCCH 600 shown in Figure 5. However, to improve a likelihood of correctly
communicating the information to mobile devices resource allocation messages for example are
transmitted using both parts of the EPDCCH 602, 604 shown in Figure 6 in order to provide some
frequency diversity. However, as will be appreciated with the example shown in Figure 6 only full
capability devices of the first type will be able to receive the distributed EPDCCH 602, 604.
Narrow Band Control Channel With Virtual Carrier Operation
Embodiments of the present disclosure have been devised to satisfy a requirement for reduced
capability devices of the second type to receive control information such as resource allocation
messages from a narrow band control channel such as the EPDCCH. As explained above with
reference to Figure 4 a virtual carrier 501 is provided for communicating with reduced capability
communications devices. To this end, as shown in Figure 7 the EPDCCH 600 is disposed by a base
station to be within a frequency range of the virtual carrier. In one example as illustrated in Figure 7,
the EPDCCH 600 is located between the shared resources provided by the virtual carrier (VC) PDSCH
701, 702. As explained above the EPDCCH 600 which forms a narrow band control channel
communicates control information to both the full capability communications devices of the first type
and reduced capability mobile devices of the second type. However, the EPDCCH 600 when
communicating resource allocation message to the reduced capability mobile communications devices
of the second type allocates resources within the virtual carrier shared resources 701, 702 whereas
when communicating resource allocation messages to the full capability mobile devices of the first
type, the resource allocation messages allocate resources within the shared resources of the host carrier
704, 706. A further example arrangement is shown in Figure 8 in which arrows 801, 802 show
respectively the allocation of resources to the mobile devices of shared resources within the virtual
carrier 801 and the shared resources within the host carrier 806.
Distributed Narrow Band Control Channel
A further example embodiment in which a narrow band control channel is provided for
operation with a virtual carrier is shown in Figure 9 . The example shown in Figure 9 is for a situation
which corresponds to the arrangement illustrated in Figure 6 of a distributed EPDCCH. Thus as
shown in Figure 9 an EPDCCH is distributed between a first part 902 and a second part 904 but
otherwise operates in a corresponding way to that explained above with reference to Figures 7 and 8.
However, as shown in Figure 9 only the first part of the EPDCCH 902 is disposed within a second
frequency range of the virtual carrier 501 whereas a second part 904 is disposed within a first
frequency range of the host carrier. Accordingly, whilst full capability mobile devices of the first type
can use a frequency diversity provided by the first and second parts of the EPDCCH 902, 904, reduced
capability mobile devices of the first type can only receive control channel messages such as resource
allocation messages from within the EPDCCH 902 of the first part. Accordingly, some adaptation of
the control channel messages communicated to the reduced capability communications devices may be
made such as increasing channel coding such as error correction coding or reducing modulation order.
As the example shown in Figure 7 and 8, the reduced capability devices receiving resource allocation
messages from the EPDCCH first part 902 will only be allocated resources within the virtual carrier
501in the shared resources 906, 908 whereas full capability devices will be allocated resources within
the shared channel 910, 912, 914.
Corresponding examples to that shown in Figure 9 are provided in Figures 10 and 1 1 where
like parts have the same numerical references. For t e example shown in Figure 10 an EPDCCH
which is distributed between two parts 906.1, 906.2 within the virtual carrier range 501 is shown.
According to this example reduced capability communications devices can be allocated resources
within the shared channel 1001 using an EPDCCH which has a first part 906.1 and second part 906.2
thereby providing some frequency diversity to the communication of the resource allocation messages.
The example shown in Figure 11 corresponds to the example of Figure 9 in which two distributed
EPDCCH parts 902, 904 are each respectively within two virtual carrier areas 501, 502.
A further variation is illustrated in Figure 12 in which a distributed EPDCCH having first and
second parts 902, 904 is adapted to communicate control information to different groups of mobile
devices. In the example shown, a first group of communications devices UEA receives control
information only from the EPDCCH first part 902 and a second group of communications devices
UEB receives control information from the EPDCCH second part 904. However, a third group of
mobile devices UEC receives control information from the first and second parts of EPDCCH 902,
904.
Common Search Space
As explained above, the narrow band control channel which in the example given is the
EPDCCH may convey some of the same information as a wide band control channel region which is
the PDCCH in this example. However, the wide band control channel, PDCCH, may convey other
information which is necessary for mobile devices to transmit via the uplink or receive via the
downlink communications signals. In one example of LTE such control channel or signalling
information is referred to as the Common Search Space information. However, as explained above for
a virtual carrier operation mobile communications devices of a reduced capability cannot receive
information from the wide band control channel PDCCH.
Embodiments of a further example include a control channel within the virtual carrier 501 for
communicating control information which is necessary for the mobile devices of reduced capability to
transmit and to receive via the wireless access interface. Three examples are illustrated of such an
arrangement in Figures 13, 14 and 15. As shown in Figure 13, which corresponds generally to the
example shown in Figure 7, and so corresponding parts contain the same numerical references, a
control channel is formed within the shared resource space 701, 702 of the virtual carrier 501 which is
shown as a darker area 1301, 1302. Thus the control channel for conveying for example Common
Search Space information is divided into a first part 1301 and a second part 1302 to provide some
frequency diversity. The arrangement of the control channel 1301, 1302 to provide Common Search
Space information which is based on the Common Search Space information communicated in the
wide band PDCCH 300 conveys to reduced capability devices necessary control information for
communicating via the shared channel on the uplink or the downlink. For example the Common
Search Space information may include information relevant to random access procedure, paging,
system information transmission, uplink transmission power control and other information necessary
for the mobile devices to communicate via the shared resource. Figure 14 provides an example
which corresponds to that shown in Figure 13 but the control channel for conveying Common Search
Space information 1301, 1302 is located in a different part of the sub-frame to that shown in Figure
13. Figure 15 provides a further example in which the control channel for conveying Common Search
Space information 1301, 1302 extends in a narrow band arrangement in time from the wide band
control channel 300 to substantially the entire part of the sub-frame.
Example Architecture
Figure 16 provides a schematic diagram showing part of an adapted LTE mobile
communications system. The system includes an adapted enhanced Node B (eNB) 1401 connected to
a core network 1408 which communicates data to a plurality of conventional LTE devices 1402 and
reduced capability devices 1403 within a coverage area (i.e. cell) 1404. Each of the reduced capability
devices 1403 has a transceiver unit 1405 which includes a receiver unit capable of receiving data
across a reduced bandwidth and a transmitter unit capable of transmitting data across a reduced
bandwidth (or full bandwidth of an uplink carrier supported by the eNB 1401) when compared with
the capabilities of the transceiver units 1406 included in the conventional LTE devices 1402.
The adapted eNB 1401 is arranged to transmit downlink data using a sub-frame structure that
includes a virtual carrier as described above for example with reference to Figures 4 to 15. The
reduced capability devices 1403 are thus able to receive and transmit data using the uplink and
downlink virtual carriers as described above.
As has been explained above, because the reduced complexity devices 1403 receive data
across a reduced bandwidth downlink virtual carriers, the complexity, power consumption and cost of
the transceiver unit 1405 needed to receive and decode downlink data and to encode and transmit
uplink data is reduced compared to the transceiver unit 1406 provided in the conventional LTE
devices.
When receiving downlink data from the core network 1408 to be transmitted to one of the
devices within the cell 1404, the adapted eNB 1401 is arranged to determine if the data is bound for a
conventional LTE device 1402 or a reduced capability device 1403. This can be achieved using any
suitable technique. For example, data bound for a reduced capability device 1403 may include a virtual
carrier flag indicating that the data must be transmitted on the downlink virtual carrier. If the adapted
eNB 1401 detects that downlink data is to be transmitted to a reduced capability device 1403, an
adapted scheduling unit 1409 included in the adapted eNB 1401 ensures that the downlink data is
transmitted to the reduced capability device in question on the downlink virtual carrier. In another
example the network is arranged so that the virtual carrier is logically independent of the eNB. More
particularly the virtual carrier is arranged to appear to the core network as a distinct cell. From the
perspective of the core network it is not known that the virtual carrier is physically co-located with, or
has any interaction with, the host carrier of the cell. Packets are routed to/from the virtual carrier just
as they would be for any normal cell.
In another example, packet inspection is performed at a suitable point within the network to
route traffic to or from the appropriate carrier (i.e. the host carrier or the virtual carrier).
In yet another example, data from the core network to the eNB is communicated on a specific
logical connection for a specific mobile device. The eNB is provided with information indicating
which logical connection is associated with which mobile device. Information is also provided at the
eNB indicating which mobile devices are reduced capability devices and which are conventional LTE
devices. This information could be derived from the fact that a reduced capability device would
initially have connected using virtual carrier resources. In other examples reduced capability devices
are arranged to indicate their capability to the eNB during the connection procedure. Accordingly the
eNB can map data from the core network to a specific mobile device based on whether the mobile
device is a reduced capability device or an LTE device.
When scheduling resources for the transmission of uplink data, the adapted eNB 1401 is
arranged to determine if the device to be scheduled resources is a reduced capability device 1403 or a
conventional LTE device 1402. In some examples this is achieved by analysing the random access
request transmitted on the PRACH using the techniques to distinguish between a virtual carrier
random access request and a conventional random access request as described above. In any case,
when it has been determined at the adapted eNB 1401 that a random access request has been made by
a reduced capability device 1402, the adapted scheduler 1409 is arranged to ensure that any grants of
uplink communications resource elements are within the virtual uplink carrier.
In some examples, the virtual carrier inserted within the host carrier can be used to provide a
logically distinct "network within a network". In other words data being transmitted via the virtual
carrier can be treated as logically and physically distinct from the data transmitted by the host carrier
network. The virtual carrier can therefore be used to implement a so-called dedicated messaging
network (DMN) which is "laid over" a conventional network and used to communicate messaging
data to DMN devices (i.e. reduced capability devices).
Various modifications can be made to examples of the present disclosure. Embodiments of the
present disclosure have been defined largely in terms of reduced capability devices transmitting data
via a virtual carrier inserted in a conventional LTE based host carrier. However, it will be understood
that any suitable device can transmit and receive data using the described virtual carriers for example
devices which have the same capability as a conventional LTE type device or devices which have
enhanced capabilities.
Furthermore, it will be understood that the general principle of inserting a virtual carrier on a
subset of uplink or downlink resources can be applied to any suitable mobile telecommunication
technology and need not be restricted to systems employing an LTE based radio interface.
Various further aspects and features of the present invention are defined in the following
numbered clauses:
1. A communications device for transmitting data to or receiving data from a mobile
communications network, the mobile communications network providing a wireless access interface
for the communications device, the communications device comprising:
a transmitter unit adapted to transmit data to base stations of the mobile communications
network via the wireless access interface provided by the base stations, wherein the wireless access
interface providing
in a downlink, a first carrier, the first carrier providing a plurality of communications resource
elements across a first frequency range for communicating data and providing a plurality of
communications resource elements within a second frequency range which is within and smaller than
the first frequency range forming a second carrier,
a plurality of time divided sub-frames, each sub-frame including the plurality of
communications resource elements of the first frequency range and the plurality of the
communications resource elements of the second frequency range, and each sub-frame includes
a first wideband control channel in a part of each sub-frame having a bandwidth
corresponding substantially to the first frequency range, and
a second narrow band control channel in a second part of each sub-frame and having a
bandwidth which is less than the first wideband control channel and; and
a receiver unit adapted to operate with a receiver band width corresponding to the second
frequency range and is configured to receive control information from the second narrow band control
channel to access the plurality of the communications resource elements of the second frequency range
of the second carrier.
2 . A communications device according to clause 1, wherein the receiver unit is
configured to receive a second resource allocation messages from t e second narrow band control
channel, the second resource allocation messages providing an indication of communications resource
elements in the second frequency range of the second carrier which have been allocated to
communications device, the resources allocated to the second mobile devices being allocated within
the second frequency range of the second carrier.
3. A communications device according to clause 1 or 2, wherein the receiver unit is
configured to receive common control information from a control channel formed within the second
frequency range of the second carrier, the common control information including signalling
information for use by the communications devices to transmit and receive data via the plurality of
communications resource elements of the second frequency range.
4 . A communications device according to clause 1, 2 or 3, wherein the communications
device is configured to operate in accordance with a Long Term Evolution (LTE) based system, and
the wide band control channel is an Physical Downlink Control Channel (PDCCH), the narrow band
control channel is an Enhanced Physical Downlink Control Channel (EPDCCH) and a plurality of the
communications resource elements form part of a Physical Downlink Shared Channel (PDSCH).
5. A method of operating a communications device to transmit data to or receive data
from a mobile communications network, the mobile communications network providing a wireless
access interface for the communications device, the wireless access interface providing, on a
downlink, a first carrier, the first carrier providing a plurality of communications resource elements
across a first frequency range for communicating data and providing a plurality of communications
resource elements within a second frequency range which is within and smaller than the first
frequency range forming a second carrier,
the method comprising:
transmitting data to base stations of the mobile communications network via the wireless
access interface provided by the base stations and
receiving data from the base stations of the mobile communications network via t e wireless
access interface provided by the base stations, wherein the data is received in a receiver band width
corresponding to the second frequency range,
the data received from the base stations being provided in a plurality of time divided subframes,
each sub-frame including the plurality of communications resource elements of the first
frequency range and the plurality of the communications resource elements of the second frequency
range, and each sub-frame includes
a first wideband control channel in a part of each sub-frame having a bandwidth
corresponding substantially to the first frequency range, and
a second narrow band control channel in a second part of each sub-frame and having a
bandwidth which is less than t e first wideband control channel and a duration of the second narrow
band control channel within the sub-frame is greater than a duration of the first wideband control
channel within the sub-frame,
and the method further comprises:
receiving control information from the second narrow band control channel to access the
plurality of the communications resource elements of the second frequency range of the second carrier.
6 . A method according to clause 5, further comprising:
receiving second resource allocation messages from the second narrow band control channel,
the second resource allocation messages providing an indication of communications resource elements
in the second frequency range of the second carrier which have been allocated to the communications
device, the resources allocated to the second mobile devices being allocated within the second
frequency range of the second carrier.
7 . A method according to clause 5 or 6, further comprising:
receiving common control information from a control channel formed within the second
frequency range of the second carrier, the common control information including signalling
information for use by the communications devices to transmit and receive data via the plurality of
communications resource elements of the second frequency range.
8. A method according to clause 5, 6 or 7, wherein the communications device is
configured to operate in accordance with a Long Term Evolution system, and the wide band control
channel is an Physical Downlink Control Channel (PDCCH), the narrow band control channel is an an
Enhanced Physical Downlink Control Channel (EPDCCH) and a plurality of the communications
resource elements form part of a Physical Downlink Shared Channel (PDSCH).
CLAIMS
1. A communications device for transmitting data to or receiving data from a mobile
communications network, the mobile communications network providing a wireless access interface
for the communications device, the communications device comprising:
a transmitter unit adapted to transmit data to base stations of the mobile communications
network via the wireless access interface provided by the base stations, wherein the wireless access
interface providing
in a downlink, a first carrier, the first carrier providing a plurality of communications resource
elements across a first frequency range for communicating data and providing a plurality of
communications resource elements within a second frequency range which is within and smaller than
the first frequency range forming a second carrier,
a plurality of time divided sub-frames, each sub-frame including the plurality of
communications resource elements of the first frequency range and t e plurality of the
communications resource elements of the second frequency range, and each sub-frame includes
a first wideband control channel in a part of each sub-frame having a bandwidth
corresponding substantially to the first frequency range, and
a second narrow band control channel in a second part of each sub-frame and having a
bandwidth which is less than the first wideband control channel and; and
a receiver unit adapted to operate with a receiver band width corresponding to the second
frequency range and is configured to receive control information from the second narrow band control
channel to access the plurality of the communications resource elements of the second frequency range
of the second carrier.
2 . A communications device as claimed in Claim 1, wherein the receiver unit is
configured to receive a second resource allocation messages from the second narrow band control
channel, the second resource allocation messages providing an indication of communications resource
elements in the second frequency range of the second carrier which have been allocated to
communications device, the resources allocated to the second mobile devices being allocated within
the second frequency range of the second carrier.
3 . A communications device as claimed in Claim 1, wherein the receiver unit is
configured to receive common control information from a control channel formed within the second
frequency range of the second carrier, the common control information including signalling
information for use by the communications devices to transmit and receive data via the plurality of
communications resource elements of the second frequency range.
4 . A communications device as claimed in Claim 1, wherein the communications device
is configured to operate in accordance with a Long Term Evolution (LTE) based system, and the wide
band control channel is an Physical Downlink Control Channel (PDCCH), the narrow band control
channel is an Enhanced Physical Downlink Control Channel (EPDCCH) and a plurality of the
communications resource elements form part of a Physical Downlink Shared Channel (PDSCH).
5. A method of operating a communications device to transmit data to or receive data
from a mobile communications network, the mobile communications network providing a wireless
access interface for the communications device, the wireless access interface providing, on a
downlink, a first carrier, the first carrier providing a plurality of communications resource elements
across a first frequency range for communicating data and providing a plurality of communications
resource elements within a second frequency range which is within and smaller than the first
frequency range forming a second carrier,
the method comprising:
transmitting data to base stations of the mobile communications network via the wireless
access interface provided by the base stations and
receiving data from the base stations of the mobile communications network via the wireless
access interface provided by the base stations, wherein the data is received in a receiver band width
corresponding to the second frequency range,
the data received from the base stations being provided in a plurality of time divided subframes,
each sub-frame including the plurality of communications resource elements of the first
frequency range and the plurality of the communications resource elements of the second frequency
range, and each sub-frame includes
a first wideband control channel in a part of each sub-frame having a bandwidth
corresponding substantially to the first frequency range, and
a second narrow band control channel in a second part of each sub-frame and having a
bandwidth which is less than the first wideband control channel and a duration of the second narrow
band control channel within the sub-frame is greater than a duration of the first wideband control
channel within the sub-frame,
and the method further comprises:
receiving control information from the second narrow band control channel to access the
plurality of the communications resource elements of the second frequency range of the second carrier.
6 . A method as claimed in Claim 5, further comprising:
receiving second resource allocation messages from the second narrow band control channel,
the second resource allocation messages providing an indication of communications resource elements
in the second frequency range of the second carrier which have been allocated to the communications
device, the resources allocated to the second mobile devices being allocated within the second
frequency range of the second carrier.
7 . A method as claimed in Claim 5, further comprising:
receiving common control information from a control channel formed within the second
frequency range of the second carrier, t e common control information including signalling
information for use by the communications devices to transmit and receive data via the plurality of
communications resource elements of the second frequency range.
8. A method as claimed in Claim 5, wherein the communications device is configured to
operate in accordance with a Long Term Evolution system, and the wide band control channel is an
Physical Downlink Control Channel (PDCCH), the narrow band control channel is an an Enhanced
Physical Downlink Control Channel (EPDCCH) and a plurality of the communications resource
elements form part of a Physical Downlink Shared Channel (PDSCH).
9 . A mobile communications device substantially as hereinbefore described with
reference to the drawings.
10. A method of communicating data to and/or from mobile communications devices
substantially as hereinbefore described with reference to the drawings.